Telephone-exchange system



No. 394,833. I,

J. F. CASEY.

2 Sheets-Sheet 1.

TELEPHONE EXCHANGE SYSTEM.

iw" M Hi!! UIN * Egtantegolf, 1888.

1 i l i (No Model.) l I E 2 Sheets-Sheet 2.

J. E. CASEY.

TELEPHONE EXCHANGE SYSTEM.

IINTTED STATES PATENT FFICE.

TELEPHONE-EXCHANGE SYSTEM,

SPECIFICATION forming part of Letters Patent No. 394,833, dated December 18, 1888. Application filed August '7, 1888. Serial No. 282,130. (No model.)

T0 all whom it may concern;

Be it known that I, JOHN F. CASEY, a citizen of the United States, residing at St. Louis, in the State of Missouri, have invented certain new and useful Improvements in Telephone-Exchange Systems, of which the following is such a full, clear, and exact description as will enable any one skilled in t-he art to which it appertains to make and use the same, reference being had to the accompanying drawings, forming part of this specification.

My invention relates more particularly to improvements in a telephone-exchange system known as the Lawsystem, which is shown and described in Letters Patent Nos. 920,8755 225,797, 278,613, 294,851, 319,856.

The object of the invention is to provide means whereby subscribers may call up the central otiice eventhough the call-circuit be broken and grounded between the subscribers and said central office. In the Law system a certain number of subscribers are located in a common call-circuit, but each subscriber is provided with an individual talking-circuit. In order for subscribers to obtain connections they first push in a button, which puts them in the call-circuit, and ask the central office for the subscriber desired. The central office signals the party desired over his talking-circuit, and then makes connection between the two subscribers. lVhen subscribers have made their call, the button is allowed to resume its normal position and returns them to the talking-circuit in which their apparatus is normally located. It rarely happens that two subscribers call over the common call-circuit at the same time; but should this happen the call of one will be superimposed upon the call of the other, and the operator will receive both calls, or, if only one is received, the othersubscriber must call again until his connection is made. In practice, however, no trouble from this cause arises.

All of the above is clearly set forth in the patents above referred to, and is alluded to herein to make the present sl'iecitication complete in itself.

The call-circuit above referred to may be a complete metallic circuit, or it may be a circuit in which the ground is used as a return, in which case the subscribers, by pushing' in their buttons before calling, connect themselves to ground and to the call-circuit, and thus complete said circuit, over which they may talk with the operator at thc central station. I will herein describe my invention as applied to the latter kind of a call-circuit, and as also applied to the Law system; but I wish to have it understood that I do not limit myself to either of the same. Said call-circuits which I have described that use the ground for a return are known, generally, as tree-wire calling-circuits, in that they consist of a mailitrunk wire with branches therefrom ruiming to the various subscribers. It often happens that said treewires become grounded between the subscribers and the central office, so that connnunication with the central office is cut off. In practice, however, the tree-wires run close to other wires, and even though the tree wires be grounded between the subscribers and the central oflice the calls will reach said central office bythe induction over the neighboring wires. It will be noted here that when a tree-wire is so grounded and the subscriber calls into it a complete circuit is formed from the subscriber to the ground by way of the tree-wire and returning' by the ground to the subscribers ground, so that the circuit is complete, and thus induction may take place between said tree-wire and the neighboring wires. Even though the treewire be not grounded the static capacity of the line will be such that when said tree-wire is used some induction will take place. IVith a ground the induction would of course be greater. It is found, however, that induction cannot be safely relied on to bring the calls to the central station. At least a safer mode of accomplishing the result is desirable, and this is the purpose of the present invention. lV hen the call-circuit is broken or grounded,

as I have described, it practically cuts a great number of subscribers from the central office, so that one break in said circuit is of more consequence than a break in the talking-circuits of several subscribers, for each one of said latter breaks cuts off but one subscriber. The importance of this subject has induced me to devise the presentinvcnt-ion, which consists, brieliy, in connecting the tree-wires with one of the talking-circuits, so that when a tree-wire becomes disrupted or grounded, as explained, the calls can be sent over the part IOO of the call-wire that intact and one of the talking-circuits, which talking-circuit is used as a call-circuit for the time being until the tree-wire can be repaired, which often takes considerable time. The colmection between a tree-wire and one ol' the talking-circuits made in such a manner as not normally to have the tree-wire interfere with the operation of said talkin g-circuit as a talkin g-circuit. does the talking-circuit when so connected with the tree-wi rc interfere materially with the funetionsof the tree-wire normally; but when the tree-wire is broken and the tal king-circuit is used to transmit calls over, the talking-circuitcannot be used Vfor talking' purposes without breaking said connection and cutting oli' the calls, so that as a matter ol fact, considering the talking-circuit alone, it may be said that `it is at all times independent ol the treewire. lhe aforesaid connection remains always intact between the tree-wire and the talkin g-ci rc ui t.

I will now describe my invention in detail by referring to the accompanying drawings, making a part hereof, in which Figure l is a diagrammatic view of the Law system provided with my improvements. Fig. ll is a diagrammatic view showing the normal position of the circuits and devices ot' a subscribers station provided with my improvements. Fig. lll shows the same circuits and devices when the telephone is oft the hook, which represents a case wherein the aforesaid subscriber is talking over his individual circuit to another subscriliier. Fig. lV represents a case wherein the telephone is oit' the hook and the switch-button is pushed in, illustrating a case wherein the subscriber has taken his telephone oli' the hook and is asking the central oflice for a connectitm.

The saine letters and figures of reference represent the same parts throughout the several views.

In practice l usually make the cimnection between the tree-wire and one of the talkingcircuits at a subscribefs station, and prel'erably with the terminal subscriber. Figs. ll, IH, IV represent therefore the apparatus at a terminal. subscribers, all the apparatus at the other subscriber bein the same, with the exception that the connection between the tree-wire and the tal ki ng-ci rcuit and th cir contacts are omitted.

Having more particular referem'fe to Fig. I, A B C represent sections ot' the Law switchboard, the section A being presided over by an operator, u, and the section B being presided over by an operator, Z). t are the fixed terminals of the switch-board, and t the flexible ternflinals of the switch-board. l have represented diagrammatieally the ffixed terminals by black dots and the tlexible terminals diagraininatically by small circles, in order toreadily distinguish the two from each other. In the patents above noted is clearly set ont the operation, function, and construction of the tixed and iiexible terminals.

Nor l l represents a tree-wire, which is connected by branch wires with subscribers S, located at various points, and 2 designates the individual talking-cireuits, which pass through the various sections of the s\vit .l1board to the various subscribers, where said wires are normally grounded. The branch circuits oli' the tree-wires are normally disconnected from theground at thesubscribers. Said subscribers by pushing' in their button, as shown in Fig. IY, connect said branch wires with the ground, and. ciinnplete the circuit ol' the treewire to ground by way ol.' the bell-magnet, &c., and also to ground by way of thei'oregoing through the telephone transmitter and receiver, when the telephone is off the hook, as shown in Fig. IV, so that conversation may be carried on over said tree-wire with the switchboard operator at the central ofticc. lf now the tree-'wire becomes grounded at any point, communication will be cut off between the subscribers between said ground and the ccntral otlice. ln order to enable me to receive such calls in spite of such a break otl circuit, I connect: the tree-wire 1l at any ol the subscribers, but preferably the tin'minal on e, with that subsm-ibefs Milking-circuit preferably by means oli' a condenser, 3, which arrangenient is shown` diagrammaticallyin Fig. l, the details thereof and thcprecise arrangement of circuits and devices being shown in the remaining figures of the drawings. ln the diagram l have represented the individual talking-circuits by broken lines, so as to distinguish them from the tree-wires more readily.

Before describing the arrangement in detail l will slate brielly how thc invention is to be inierated, so to more clearly set it forth. 'hcn a break occurs in the tree-wim, this fact, oi' course, becomes at once known to the operator presiding over said tree-wire at the central otlice. ll is known, ol' course, which talking-circuit is provided wit h the condenserconnection, and lv may say here in practice IA select a talking-circuit for this purpose, which is comliaratively idle, so that the invention maybe carried out with greater success. ',lhe o1r erator, knowing that her tree-wire is out of circuit, innnediately inserts plug 1-, which is ctmnected with her .receiver in the fixed ierminal f ol' the talking-circuit which is to be used to receive the calls over. This is clearly shown in the lower halt' ot' Fig. l. rlhe plug shown in the upper part of Fig. I is in its normal disconnected position. \\'hen the above connection is iliade, the calls may be received from the subscribers over the talking-cireuit in the operatoi"s receiver, which is suitztbly connecteifl to ground. 'vlhus all the calls between the break and the central office are'received over the tree-wire, as before, so that every call sent in is receivedwithout interruption or diminution in volume and force at the central office.

In order now to explain how the condenserconnection does not interfere with the normal IOO IIO

operation of the lines and to set forth the construction and operation of the devices connected therewith recourse must be had to Figs. II, III, and IV.

1 is a branch of the tree-wire as it enters a subscribers station, and 2 is an individual talking-circuit, as before.

G is a switch which terminates in a button, 5, before referred to. This switch consists of plates 7 and S, mounted upon an insulatingbase, 9. Adjacent to these plates are two plates 10 and 1l, also mounted upon the base 9, the whole being moved by the button 5.

12 12 are two spiral springs, which are connected with extensions of the plates 7 and S and operate to draw the switch to its normal position when pushed in by the button 5.

13 1t are springs which normally rest upon the plate 10, and l5 and 1G are springs which normally rest upon the plates 7 and S, respectively. The tree-wire 1 is connected to the spring lait, and the spring 13 to the condenser The spring 15 is in communication with the telephone-hook and the spring 16 with the talking-circuit. Around the telephonehook are arranged four contacts, 17, 1S, 19, and 20, the two former being below said hook and the two latter bein above the same. The contact 17 is connected to the other plates of the condenser 3, and the contact 1S is connected with the transmitter T, and also in electrical connn'unication with one of the spiral springs 12 and plate S. The contacts 19 and 20 are in electrical communication with the local circuit of the transmitter T, the said circuit being shown in dotted lines in ordfr to distinguish the saine more readily. \Vhen the telephone is taken from the hook, the hook rises and completes the circuit of the local battery L13 through the transmitter T. The terminal 19 is connected also through a bell-magnet, 2l, to ground. A circuit, 22, connects the wire between the spring 15 and the telephone-hook with a spring that normally rests upon the armature 4of the bellmagnet 2l, which armature is also connected to the ground through the bell-magnet.

All of the foregoing shown in Figs. 11, III, and IV, excepting the condenser, condenserbranch, and its contacts, malte no part of my invention, the same being of the ordinary construction.

Fig. Il shows the parts in their normal position, and illustrates how the calls are received at the subscribers and pass over the condenser branch to the talking-circuit 2 when the tree-wire is broken. The calls pass from the treefwire l to the spring 14 over the plate 9 to the spring 13, charging the con denser 3, which charges the opposite plate thereof andlcauses a current to pass to the contact 17, to the tele1i honehoolt, to ground by way of the circuit 22, armature, and bellmagnet, and also from said telephone-hook to the contact 1S, over spiral spring l2 to plate 8 and spring 16 to the talking-line 2, to plugl 4, and operat ors telephone and ground, as shown in Fig. I. The current passing to ground by way of the bell-magnet and wire 22 will be Wasted, but the current passing to contact 18 and line 2 will be sufficient to cause the call to be heard in the central office operators receiver. Then the subscriber having this condenser branch connected around his apparatus is signaled from the central office and his apparatus is in its normal position, as shown in Fig. Il, the current passes in a reverse direction to that set forth and indicated by the arrows in Fig. Il as vfar as contact 18, from whence it passes through lthe bell-magnet to ground in the same direction, indicated by the arrows. The greater portion of said current passes to grouml through the bell-magnet by way of circuit and bellmagnet-armatu re and rings up the subscriber, and the remaining portion passes to the condenser and line 1. This latter portion will not be sufficient to disturb the Vfunctions of the tree-wire, but will have butlittle effect on said tree-wire, the condenser being of much higher resistance than the bell-magnet. It will be noted also, as remarked above, that I select purposely an individual talking-circuit that is used but very little. Consequently such a wire would rarely be used for talking purposes, and hence but few signals would be sent over said wire from the cent-ral office, and even when so sent they would not materially interfere with the function of the tree-wire. Such a talking-wire could be used as a callcircuit the greater part of the time without having its functions interfered with at all. To obviate this entirely, the operators at the central station would notify the subscriber that his circuit was not to be used as a talking-circuit until the tree-wire was repaired, and the operators would not signal over the talkin g-circuits that are being so used. They would not call up such subscriber at all, but merely inform others desiring to talk with such subscribers that they cannot do so for the present.

I will ment-ion here that any number of subscribers may he provided with a connection between the tree-'wire and their talkingcir cuits, .fo that should one subscribers line be out of orler the calls may be still received over another subscribers ta]king-circuit. As a iratt r of fact, it would not matter if each subscriber was provided with such a connection; but in practice one or two subscribers provided with the connection will be found to answer all requirements. Where more than one connection is made between a treeavire and the talkingcircuits and the subscriber whose wire is being used temporarily to receive calls over is asked for by another subscriber, the operator can withdraw plug 4 from the former subscribers circuit and connect said plug -l with another subscribers circuit, which has the condenser-connection, and can then'connect together the two form er subscribers. In this way the subscribers whose circuits are used in cases of emergency as call- IIO circuits are not inconveniellccd ill the sliglltest, it not even being necessary in tllis instance to sacrifice the one Afor the nlally, as mentioned below.

Fig. Ill shows the telephone olf the hook, the subscriber being supposed to be talking over his circuit to allotller subscriber. In this instance the condenser branch is broken at the contact i7. inlseq llently the tree-wires can nevel' interfere with the individual wires when used for talking purposes. The talking-circuit, ill this condition of affairs, sllould not be llsed lo selld calls over. In practice Vwhen the tree-wire is ollt of order alld connection is nlade with the talking-circuit by lnealls of the plug 1t, as described, the subscriber witll whose talking-circuit connection is lnade will be notified by the central office that llc cannot use his telepllolle ulltil the tree-wire is repaired, sacriflcillg the one sllbscriber for the tilne being for the good of the lllany. It will be noted that wllell the treewire is ill order and the subscribel"s wire is not being used as a call-circuit the sub scriber may use his talkil'lg-circuit tlle salne as before. The arrows ill Fig. III sllow the direction of the current, the current passing ill this instance fronl the transmitter T to spiral spring 12, plate S, sprillg lf3, alld line to celltral office operators receiver, to grou nd by way of sallle, to the bell-lllagnet 2l, colltact lil, telephone-hook through telephol'le-receiver alld back to telephone transmitter. The contact 1S alld telephonehook when ill collllllunication with each otller act to short circuit the receiver and translnilter. This is the usual function of these parts alld is no part ol' nly invention. Sllould the celltral oliice signal the subscriber over his talking-circuit while his telepllolle is off the hook, the currellt will pass over the circuit indicated by the arro\ Ys ill a reverse direction to that shown by said arrows and cause the bell to give one tap. Tllis gives ille operator at the celltral office the busy test. This test is described ill the patents aforesaid, alld is also clearly set ont ill the application ol.' YDnrallt and Bailey, Serial No. 27i,l-2:i, liled May 10,15%. In this illstallce none of the sigllalillgcurrent passes over the condenser branch or tree-wire, as the circuit thereof is broken at the contact i7. In case the subscriber wishes lo talk to the central oflice when the tree-wire is broken and his circuit is being used asa callcircuit, he could do so, as clearly sllowll ill Fig. III, without pushing ill his button 5, but this would illterfere with the calls, as poillted out above. In this case he would talk to the central office over his talking-circuit alld not over the tree-wire as ordinarily, for the celltral office operatol"s receiver is now in the circuit of his talking-wire, (see Fig. L) so tllat the subscriber having the condenser-conllectioll around his instrulnent is not as a nlatter of fact cut off fronl the central office whell his talking-circuit is being used as a call-wire.

In Fig. IV thc but-ton 5 is represented as having been pushed ill, which brillgs the springs 1 3 alld lat on the plates 7 and S, respectively, and the sprillgs ,l5 and 16 both upon the plate ll, conlpletillg the circuit betweell thcln. This represents the collditioll of affairs when the tree-wire is in order alld the subscribel.' is calling the central office over said tree-wire for the purpose of getting a collllectioll with another subscriber. If the tree-wire were broken, the subscriber could not, of course, conllnunicatc with the central office when his button was pushed ill, as showll ill Fig. IV, but could do so by allowing his button to resullle its llol'lnal position, as just pointed out above and showll ill Fig. III. The arrows show the path of the current under the condition of cireunlstallces shown ill Fig. IV. The current passes ill this instance fronl the transmitter T over the spiral spring l2, the plate S, the tree-wire l, and ground, by way of sallle to the bell-magnet 2l, by way of telephone-hook and circuit 22110 transn nlitter and back to receiver. Should a sigllal be sellt over the lille 2 fronl the central office in this case, the current will, pass from the sprill lll by way of the platel l, to the spring l5, alld fronl thence to ground by the telephone-hook and bell-magnet. The bell will give one tap, as before, and the busy test will be given to the operator at the cel'ltral oliice. None of the signaling-currellt can pass over the condenser branch, Afor as ill the previous instance the circuit thereof is broken at the colltaet I7. The circuit 22 lllerely acts to lnake alld break the bellslnagnet circuit when the telephone-hook is ill the position shown in Fig. II-that is, it lnakes the bell-magnet avibrating one, the saine acting as a rheo tolne.

I do not wish to lilnit nlyself to a condenser to nlake connection between a treewire alld one of the talking-circuits, as any other kind of device having the salne function could be used and still be 'within nly invention. For instance, an induction-coil of high resistance could be used in lieu thereof, if desired. So, also, any nleans of switching alld controllillg the circuit at the subscribers station could be used. Likewise, any other lneans of connecting the switch-board operators re ceiver with the talkin g-circnit, instead of the plug 4 all d connecting-wire, could be used and. still be within nly invention. I do not wish, therefore, to lilllit nl ysel'f to the exact devices and arrangenlent set forth.

Ilaving now fully set forth lny invention l and described its operation alld usefulness,

what I desire to claln alld secure by Letters Patent of the United States as lny invention isl. The colllbillatioll, with a telephoneelirchange systenl having talkillg-circuits and call-circuits independent thereof, of all electrical connection between any of said call-circuits alld one or lllore of the talkillg-cireuits, whereby when any of the call-circuits becolne IOO IIO

impaired the independent talking-circuits may be used as call-circuits.

2. The combination with a telephone-exchange system having,` talking-circuits and call-circuits, ot an electrical connection normally intact between said call-circuit and one or more of the talkin g-circuits, whereby when the call-circuit becomes impaired the talkin gcircuit may be used as a call-circuit.

3. A telephone-exchange system havingl a tree-wire call-circuit, as described, common to several subscribers, individual talking-circuits from said subscribers to the central oli-ice, and one or more electrical connections between said tree-wire and said talking-circuits, :tor the purpose described. Y

4. The combination, with a telephone-exchange system, of a tree-wire calling-circuit passing' to a number ot' subscribers and normally disconnected from the ground, as usual, individual talking-circuits connecting' said subscribers with the central otlice and normally `grounded at said subscribers, one or more electrical connections between said treewire and one or more said individual talkingcircuits, respectively, and means t'or connecting' the switch-board opcrators receiver with said individual talking-circu it, for the purpose described.

5. The combination, with a call-circuit and a talking-circuit, ot' an electrical connection normally intact between the two, whereby when the calling-circuit becomes grounded the talking-circuit can be used to transmit the calls sent over the calling-circuit, substantially as and tor the purpose described.

0. The combination, with a telephone-exchange system ot' thetype described, of a tree-wire calling-circuit ot' the character set forth, common to a number oi' subscribers, individual talking-circuits passing from said subscribers to the central office and suitably grounded at said subscribers, a condenser branch between said tree-wire calling-circuit and one ot' said talking-circuits, and a plugl connected with the switch-board operators receiver, adapted to connect said receiver with said talking-circuit, substantially as and for the purpose described.

7. The combination, with a telephone-ex 5o change system, of a tree-wire calling-circuit of the character described, common to a number of subscribers,individual talking-circuits grounded at t-he subscribers and passing to the cent-ral office, a subscribers switch-button adapted to connect said subscriber with the tree-wire calling-circuit or with the talking'- circuit at will, a telephone-hook provided with the usual contacts, as set-forth, an additional contact therefor, and a condenser and condenser branch between the tree-wire calling-circuit and said contact, substantially as and 'for the purpose described.

8. The combination, with a telephone-exchange system of substantially the character described, of a tree-wire calling-circuit, as l, individual talking-circuits emanatingfrom a central office and grounded at the subscribers, one or more subscribers sub-stations provided with a switch, consistingI ot' plates 7, 8, l0, and l1, insulated from each other, and spring-terminal li, connected with the treewire and normally bearing' on the plate l0, the spring 1S, also normally bearingI on said plate l0, means t'or nlaintaining said switch in its normal posit-ion, springs l5 and 1G, bearing,I upon the plates 7 and 8 normally, and a push-button, as 5, operatingx said plates, a condenser branch and condenser connected with XVitnesses:

A. C. FowLER, THOMAS M. GRACE. 

